Monday, September 9, 2013

New paper finds South America was warmer & had more severe drought 6,000 years ago in comparison to modern climate

A paper published today in Climate of the Past compiles 120 paleoclimatological datasets from eastern South America and finds the climate was warmer ~6,000 years ago "when compared to the modern climate." The authors also find drought was much more severe, lake levels lower, and vegetation less 6,000 years ago in comparison to modern climate. 

When compared to modern climate, our compilation indicates a deficit in the water balance in eastern South America during the Mid-Holocene. With diminished precipitation and enhanced evaporation (less cloudiness), the lake levels were below their modern levels, and air temperatures near the surface were above modern values. These higher air temperatures can be related to less vegetation and to a higher surface albedo.

Clim. Past, 9, 2117-2133, 2013

A mid-Holocene climate reconstruction for eastern South America
L. F. Prado1, I. Wainer1, C. M. Chiessi2, M.-P. Ledru3, and B. Turcq4
1Instituto Oceanográfico, Universidade de São Paulo, São Paulo, Brazil
2Escola de Artes, Ciências e Humanidades, Universidade de São Paulo, São Paulo, Brazil
3IRD UMR 226 Institut des Sciences de l'Evolution, IRD CNRS UM2, Montpellier, France
4IRD UMR 7159 Laboratoire d'Océanographie et du Climat: Expérimentations et approches numériques, Bondy, France

Abstract. The mid-Holocene (6000 calibrated years before present) is a key period in palaeoclimatology because incoming summer insolation was lower than during the late Holocene in the Southern Hemisphere, whereas the opposite happened in the Northern Hemisphere. However, the effects of the decreased austral summer insolation over South American climate have been poorly discussed by palaeodata syntheses. In addition, only a few of the regional studies have characterised the mid-Holocene climate in South America through a multiproxy approach. Here, we present a multiproxy compilation of mid-Holocene palaeoclimate data for eastern South America. We compiled 120 palaeoclimatological datasets, which were published in 84 different papers. The palaeodata analysed here suggest a water deficit scenario in the majority of eastern South America during the mid-Holocene if compared to the late Holocene, with the exception of northeastern Brazil. Low mid-Holocene austral summer insolation caused a reduced land–sea temperature contrast and hence a weakened South American monsoon system circulation. This scenario is represented by a decrease in precipitation over the South Atlantic Convergence Zone area, saltier conditions along the South American continental margin, and lower lake levels.

No comments:

Post a Comment